In an interview before he was convicted, Cheung, 28, told the Sunday Morning Post how X gave him the love denied to him by his own father, regularly held hands with him in public and looked after him 'like a son' by making him congee when he was sick.

In the interview, and in court testimony, Cheung also revealed the less savoury side of this so-called father-son relationship. The bright student sought to explain how simple piano playing, for which the pair shared a passion, developed into intimate bathing sessions and more.

Cheung denies he is a homosexual and says he has had a girlfriend for years, even during the time of his sexual liaisons with X.

He also talked of the involvement of a key figure in the blackmail plot, a women very much his senior who police have identified - but not charged - as his co-conspirator in making the blackmail demand of HK$6 million to X.

It was this woman, Li Dora Kay, who Cheung claims planted the seed of extortion in his mind and took him under her wing when he began to feel uncomfortable and exploited by his relationship with X.

Ironically, the court heard, it was X who brought Cheung and Li together after a chance meeting in the street.

Fifteen years ago Cheung had known and revered X when he was a 12-year-old Form One student at a school where X worked. They had never spoken, but when Cheung joined the school's management committee in early 2008 as an elected representative of alumni, the two hit it off immediately.

Cheung told the Post he found in X the love his father failed to give him: 'My relationship with X was like father and son. He filled the missing parts of my life. X was good to me. I remember when I was sick he would make congee for me and called on my home.

'He showed care for me and was thoughtful. I was moved. That's why I called him 'dad' or 'father' and he would call me 'good son'.'

Li, Cheung and X became friends, and Cheung says Li, who had known X for many years, puzzled over why X liked to hold Cheung's hand but explained it away by presuming they were close in a father-and-son way.

At first, Cheung would go to X's dormitory to play piano. The student held a Trinity Guildhall piano diploma and X appeared to be an even more accomplished pianist. Cheung says he admired the talented old man.

However, he claims events took a sinister turn a few months later when X started to ask Cheung to help him wash his hair because he was 'old and sick', and the two started to travel together to the mainland.

On a trip to Beijing in November 2008, the two bathed each other intimately. Later, Cheung claims, X said he fondled him because he had shown arrogance by flexing his muscular arms and X had to 'blunt his overconfidence'.

By January last year, Cheung says, he began to feel upset about what he began to see as 'sexual assaults'. He started to decline invitations to visit X and says he wanted to 'escape from the hand of the devil', the court was told.

X then suggested he pay Cheung HK$3,000 a month so that Cheung could visit his dorm room more often rather than working. Cheung told police he found this demeaning.

It was at this point that Li - who Cheung by this time was calling 'auntie' - suggested the blackmail plot and Cheung took the bait.

Using spy cameras hidden in pens at Li's prompting, Cheung taped a 72-minute film of various sex acts between himself and X, and then the blackmail approaches were made to X and his boss, who has been identified throughout only as Y.

Cheung, who was certainly physically able enough to rebuff X's advances gives this explanation for his actions: 'X was a school manager. He was revered and admirable to me. Since I was young, he had an authoritative image in my mind. I just can't explain why I didn't reject his 'assault'. I admit I was too naive,' he told the Post.

Li was also an influence, he said. 'She appeared as a heroine when I was confused and desperate for help. At that point, I was really grateful for her. She is older, mature and more sophisticated than me, so I trusted her as a young man.'

Despite Cheung's claim that he was reluctant to take part in the sex acts, the video suggested differently. He was seen laughing, chatting and cracking dirty jokes while indulging in them.

They talked about investment and discussed the words and deeds of legislator Leung Kwok-hung and Chief Secretary Henry Tang Ying-yen.

It was on the day after X's birthday that Cheung and Li hit X with the blackmail bombshell. It was to trigger payments, in cash, that eventually amounted to HK$811,000.

Like much of the story, the whereabouts of the cash remains a mystery. Despite repeated requests, the police will not say if it has been retrieved in part or in full.

Meanwhile Li, who has not been charged with any crime, has gone to ground while on police bail.

'I trusted her like a senior member of the family. I never expected that she would lead me to do something improper. I'm disgusted with what she did,' Cheung said. 'I have been looking for her in the hope of bringing her to give evidence in court. But she simply vanished.'